WIP: Initial state handling for swap process.
The state is saved to a preference file, but that is abstracted from
the SwapWorkflowActivity. It interacts with a SwapState object, which
is relatively safe in that you should not be able to save it into an
Note: At this point it is not tied to any service. I'm not sure it will
ever have to be either, as the service needs to persist state somewhere
anyway, so that will probably also end up saving to a preferences file